Date:	Fri, 10 Jan 2014 12:00:59 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
	Luigi Semenzato <semenzato@...gle.com>
Subject: Re: [PATCH -next] zram: do not pass rw argument to
 __zram_make_request()

On (01/10/14 16:14), Minchan Kim wrote:
> On Thu, Jan 09, 2014 at 04:23:43PM +0300, Sergey Senozhatsky wrote:
> > Do not pass rw argument down the __zram_make_request() -> zram_bvec_rw()
> > chain, decode it in zram_bvec_rw() instead. Besides, this is the place
> > where we distinguish READ and WRITE bio data directions, so account zram
> > RW stats here, instead of __zram_make_request(). This also allows to
> > account a real number of zram READ/WRITE operations, not just requests
> > (RW request may end up in a number of zram RW ops with separate
> > locking, compression/decompression, slot free handling, etc).
> 
> Looks sane to me because other statistic variable accounts per bio, not
> request. But it changes current statistic's semantic so they could be
> regressed. Let's wait a bit for other's opinion.
> 

Hello,

well, imho current zram stats are a bit meaningless and misleading. some data
simply makes a little sense, some data is not visible to end user at all, etc. my
plan was to revisit it before 3.14 merge window (which is also the end of promotion,
I guess). after 3.14 merge window we will not be able to change this easily.

I was going to publish stats rework patch today. It removes code duplication
and re-organizes end user visible stats. so here it is (w/o the proper commit
message)

	num_reads
	num_writes
	pages_stored
	invalid_io
	notify_free
	pages_zero
	compressed_size
	memory_used

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

---

 drivers/block/zram/zram_drv.c | 171 +++++++++++-------------------------------
 drivers/block/zram/zram_drv.h |  15 ++--
 2 files changed, 51 insertions(+), 135 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 798793f..234e703 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -42,6 +42,17 @@ static struct zram *zram_devices;
 /* Module params (documentation at end) */
 static unsigned int num_devices = 1;
 
+#define ZRAM_ATTR_RO(name)						\
+static ssize_t zram_attr_##name##_show(struct device *d,		\
+				struct device_attribute *attr, char *b)	\
+{									\
+	struct zram *zram = dev_to_zram(d);				\
+	return sprintf(b, "%llu\n",					\
+		(u64)atomic64_read(&zram->stats.name));			\
+}									\
+static struct device_attribute dev_attr_##name =			\
+	__ATTR(name, S_IRUGO, zram_attr_##name##_show, NULL);
+
 static inline int init_done(struct zram *zram)
 {
 	return zram->meta != NULL;
@@ -52,97 +63,31 @@ static inline struct zram *dev_to_zram(struct device *dev)
 	return (struct zram *)dev_to_disk(dev)->private_data;
 }
 
-static ssize_t disksize_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%llu\n", zram->disksize);
-}
-
-static ssize_t initstate_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%u\n", init_done(zram));
-}
-
-static ssize_t num_reads_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%llu\n",
-			(u64)atomic64_read(&zram->stats.num_reads));
-}
-
-static ssize_t num_writes_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%llu\n",
-			(u64)atomic64_read(&zram->stats.num_writes));
-}
-
-static ssize_t invalid_io_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%llu\n",
-			(u64)atomic64_read(&zram->stats.invalid_io));
-}
-
-static ssize_t notify_free_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%llu\n",
-			(u64)atomic64_read(&zram->stats.notify_free));
-}
-
-static ssize_t zero_pages_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%u\n", zram->stats.pages_zero);
-}
-
-static ssize_t orig_data_size_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+static ssize_t memory_used_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
+	u64 val = 0;
 	struct zram *zram = dev_to_zram(dev);
+	struct zram_meta *meta = zram->meta;
 
-	return sprintf(buf, "%llu\n",
-		(u64)(zram->stats.pages_stored) << PAGE_SHIFT);
+	down_read(&zram->init_lock);
+	if (init_done(zram))
+		val = zs_get_total_size_bytes(meta->mem_pool);
+	up_read(&zram->init_lock);
+	return sprintf(buf, "%llu\n", val);
 }
 
-static ssize_t compr_data_size_show(struct device *dev,
+static ssize_t disksize_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
 	struct zram *zram = dev_to_zram(dev);
-
-	return sprintf(buf, "%llu\n",
-			(u64)atomic64_read(&zram->stats.compr_size));
+	return sprintf(buf, "%llu\n", zram->disksize);
 }
 
-static ssize_t mem_used_total_show(struct device *dev,
+static ssize_t initstate_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
-	u64 val = 0;
 	struct zram *zram = dev_to_zram(dev);
-	struct zram_meta *meta = zram->meta;
-
-	down_read(&zram->init_lock);
-	if (init_done(zram))
-		val = zs_get_total_size_bytes(meta->mem_pool);
-	up_read(&zram->init_lock);
-
-	return sprintf(buf, "%llu\n", val);
+	return sprintf(buf, "%u\n", init_done(zram));
 }
 
 static int zram_test_flag(struct zram_meta *meta, u32 index,
@@ -289,7 +234,6 @@ static void zram_free_page(struct zram *zram, size_t index)
 {
 	struct zram_meta *meta = zram->meta;
 	unsigned long handle = meta->table[index].handle;
-	u16 size = meta->table[index].size;
 
 	if (unlikely(!handle)) {
 		/*
@@ -298,21 +242,14 @@ static void zram_free_page(struct zram *zram, size_t index)
 		 */
 		if (zram_test_flag(meta, index, ZRAM_ZERO)) {
 			zram_clear_flag(meta, index, ZRAM_ZERO);
-			zram->stats.pages_zero--;
+			atomic64_dec(&zram->stats.pages_zero);
 		}
 		return;
 	}
 
-	if (unlikely(size > max_zpage_size))
-		zram->stats.bad_compress--;
-
 	zs_free(meta->mem_pool, handle);
-
-	if (size <= PAGE_SIZE / 2)
-		zram->stats.good_compress--;
-
-	atomic64_sub(meta->table[index].size, &zram->stats.compr_size);
-	zram->stats.pages_stored--;
+	atomic64_sub(meta->table[index].size, &zram->stats.compressed_size);
+	atomic64_dec(&zram->stats.pages_stored);
 
 	meta->table[index].handle = 0;
 	meta->table[index].size = 0;
@@ -352,7 +289,7 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 			  u32 index, int offset, struct bio *bio)
 {
-	int ret;
+	int ret = -EINVAL;
 	struct page *page;
 	unsigned char *user_mem, *uncmem = NULL;
 	struct zram_meta *meta = zram->meta;
@@ -393,6 +330,8 @@ out_cleanup:
 	kunmap_atomic(user_mem);
 	if (is_partial_io(bvec))
 		kfree(uncmem);
+	if (ret)
+		atomic64_inc(&zram->stats.failed_reads);
 	return ret;
 }
 
@@ -440,7 +379,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		/* Free memory associated with this sector now. */
 		zram_free_page(zram, index);
 
-		zram->stats.pages_zero++;
+		atomic64_inc(&zram->stats.pages_zero);
 		zram_set_flag(meta, index, ZRAM_ZERO);
 		ret = 0;
 		goto out;
@@ -469,7 +408,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	}
 
 	if (unlikely(clen > max_zpage_size)) {
-		zram->stats.bad_compress++;
 		clen = PAGE_SIZE;
 		src = NULL;
 		if (is_partial_io(bvec))
@@ -503,17 +441,12 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 	meta->table[index].handle = handle;
 	meta->table[index].size = clen;
-
 	/* Update stats */
-	atomic64_add(clen, &zram->stats.compr_size);
-	zram->stats.pages_stored++;
-	if (clen <= PAGE_SIZE / 2)
-		zram->stats.good_compress++;
-
+	atomic64_add(clen, &zram->stats.compressed_size);
+	atomic64_inc(&zram->stats.pages_stored);
 out:
 	if (is_partial_io(bvec))
 		kfree(uncmem);
-
 	if (ret)
 		atomic64_inc(&zram->stats.failed_writes);
 	return ret;
@@ -594,23 +527,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 
 static void zram_init_device(struct zram *zram, struct zram_meta *meta)
 {
-	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
-		pr_info(
-		"There is little point creating a zram of greater than "
-		"twice the size of memory since we expect a 2:1 compression "
-		"ratio. Note that zram uses about 0.1%% of the size of "
-		"the disk when not in use so a huge zram is "
-		"wasteful.\n"
-		"\tMemory Size: %lu kB\n"
-		"\tSize you selected: %llu kB\n"
-		"Continuing anyway ...\n",
-		(totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10
-		);
-	}
-
 	/* zram devices sort of resembles non-rotational disks */
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
-
 	zram->meta = meta;
 	pr_debug("Initialization done!\n");
 }
@@ -803,14 +721,15 @@ static DEVICE_ATTR(disksize, S_IRUGO | S_IWUSR,
 		disksize_show, disksize_store);
 static DEVICE_ATTR(initstate, S_IRUGO, initstate_show, NULL);
 static DEVICE_ATTR(reset, S_IWUSR, NULL, reset_store);
-static DEVICE_ATTR(num_reads, S_IRUGO, num_reads_show, NULL);
-static DEVICE_ATTR(num_writes, S_IRUGO, num_writes_show, NULL);
-static DEVICE_ATTR(invalid_io, S_IRUGO, invalid_io_show, NULL);
-static DEVICE_ATTR(notify_free, S_IRUGO, notify_free_show, NULL);
-static DEVICE_ATTR(zero_pages, S_IRUGO, zero_pages_show, NULL);
-static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
-static DEVICE_ATTR(compr_data_size, S_IRUGO, compr_data_size_show, NULL);
-static DEVICE_ATTR(mem_used_total, S_IRUGO, mem_used_total_show, NULL);
+static DEVICE_ATTR(memory_used, S_IRUGO, memory_used_show, NULL);
+
+ZRAM_ATTR_RO(num_reads);
+ZRAM_ATTR_RO(num_writes);
+ZRAM_ATTR_RO(pages_stored);
+ZRAM_ATTR_RO(invalid_io);
+ZRAM_ATTR_RO(notify_free);
+ZRAM_ATTR_RO(pages_zero);
+ZRAM_ATTR_RO(compressed_size);
 
 static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_disksize.attr,
@@ -818,12 +737,12 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_reset.attr,
 	&dev_attr_num_reads.attr,
 	&dev_attr_num_writes.attr,
+	&dev_attr_pages_stored.attr,
 	&dev_attr_invalid_io.attr,
 	&dev_attr_notify_free.attr,
-	&dev_attr_zero_pages.attr,
-	&dev_attr_orig_data_size.attr,
-	&dev_attr_compr_data_size.attr,
-	&dev_attr_mem_used_total.attr,
+	&dev_attr_pages_zero.attr,
+	&dev_attr_compressed_size.attr,
+	&dev_attr_memory_used.attr,
 	NULL,
 };
 
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 1388bad..6b00d4d 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -64,8 +64,7 @@ enum zram_pageflags {
 struct table {
 	unsigned long handle;
 	u16 size;	/* object size (excluding header) */
-	u8 count;	/* object ref count (not yet used) */
-	u8 flags;
+	u16 flags;
 } __aligned(4);
 
 /*
@@ -73,17 +72,15 @@ struct table {
  * All modifications to 32bit counter should be protected by zram->lock.
  */
 struct zram_stats {
-	atomic64_t compr_size;	/* compressed size of pages stored */
-	atomic64_t num_reads;	/* failed + successful */
-	atomic64_t num_writes;	/* --do-- */
+	atomic64_t num_writes;	/* number of writes */
+	atomic64_t num_reads;	/* number of reads */
+	atomic64_t pages_stored;	/* no. of pages currently stored */
+	atomic64_t compressed_size;	/* compressed size of pages stored */
+	atomic64_t pages_zero;		/* no. of zero filled pages */
 	atomic64_t failed_reads;	/* should NEVER! happen */
 	atomic64_t failed_writes;	/* can happen when memory is too low */
 	atomic64_t invalid_io;	/* non-page-aligned I/O requests */
 	atomic64_t notify_free;	/* no. of swap slot free notifications */
-	u32 pages_zero;		/* no. of zero filled pages */
-	u32 pages_stored;	/* no. of pages currently stored */
-	u32 good_compress;	/* % of pages with compression ratio<=50% */
-	u32 bad_compress;	/* % of pages with compression ratio>=75% */
 };
 
 struct zram_meta {

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